1. Field of the Invention
This invention relates to the use of an improved catalyst for producing aromatic hydrocarbons from non-aromatic hydrocarbons.
2. Description of the Previously Published Art
The zeolites ZSM-5 and ZSM-11, first described in U.S. Pat. No. 3,702,886 and U.S. Pat. No. 3,709,979, respectively, have been extensively investigated during recent years. These zeolites have more recently been given the designation MFI and MEL zeolites, respectively, in "Chemical Nomenclature, and Formulation of Compositions of Synthetic and Natural Zeolites" IUPAC yellow booklet, 1978. Together, the materials make up the family of the "pentasil" zeolites as discussed in Jacobs, P. A., and Martens, J. A. "Synthesis of High-Silica Aluminosilicate Zeolites" Studies in Surface Science and Catalysis, Vol. 33, Elsevier, New York, N.Y., 1987, Chapter IV. There are several patents which describe compositions involving nickel-containing MFI zeolites. For example, U.S. Pat. No. 4,377,503 teaches that a novel shape-selective catalyst can be prepared by incorporating nickel into zeolites such as MFI zeolite. This patent claims only the method of producing the catalyst, and does not specify use of such a material in an aromatization process. The patent also does not recognize the ability of nickel to improve the activity of aromatization catalysts after hydrothermal treatments. U.S. Pat. No. 4,551,438 describes a catalyst for oligomerizing olefins over Ni-MFI zeolite and a hydrocarbyl aluminum halide. The catalyst of the present invention does not contain a hydrocarbyl aluminum halide. U.S. Pat. No. 4,766,265 relates to a process for the conversion of ethane to liquid aromatic hydrocarbons using a gallium modified MFI zeolite promoted with rhenium and nickel. The catalysts of the present invention do not contain gallium or rhenium. U.S. Pat. No. 4,543,347 relates to a catalyst for the conversion of synthesis gas to hydrocarbons using a catalyst that is a mixture of zinc oxide, an oxide of gallium or indium, and possibly nickel supported on MFI zeolite. The composition of the present invention, however, does not contain zinc or gallium or indium.
There are a number of processes for the conversion of hydrocarbons using Ni supported on MFI or MEL zeolites that have been claimed previously. Many of these processes using Ni-MFI and Ni-MEL zeolites are distinctly different from the process of the present invention, the aromatization of non-aromatic hydrocarbons. The use of Ni-MFI and Ni-MEL zeolites for the cracking of paraffinic feedstocks is described in the related case U.S. application Ser. No. 449,656, filed Dec. 11, 1989. Two patents, U.S. Pat. No. 4,229,282 and U.S. Pat. No. 4,642,176 describe dewaxing processes using MFI zeolite with a nickel component. These dewaxing processes are fundamentally different from the aromatization process of the instant invention because they use a feedstock, a hydrocarbon oil, that boils above 350.degree. F. (177.degree. C.) instead of the light gas (C1-C5 hydrocarbon) feedstock of the present invention. Furthermore, the dewaxing processes generally operate at elevated pressures of from 200 to 2000 psig (1.38 to 13.3 MPa) in the presence of hydrogen. U.S. Pat. No. 4,816,538 describes a hydrocracking process for producing high octane gasoline using nickel on zeolites such as MFI zeolite. This hydrocracking process is fundamentally different from the aromatization process of the instant invention because it uses a feedstock, a hydrocarbon oil, that boils above 550.degree. C., which is different from the light gas feedstock of the present invention. Furthermore, the hydrocracking process usually involves reaction at high pressures 1000 to 3000 psig (6.89 to 20.67 MPa) in the presence of hydrogen. There are several patents which describe processes for the conversion of light hydrocarbons, usually C1 to C5 hydrocarbons, to higher boiling hydrocarbons such as C5 to C12 hydrocarbons using nickel containing MFI catalysts. For example, U.S. Pat. No. 4,517,396 claims a process for converting C2 to C5 olefins into middle distillates over Ni-MFI. The process claimed involves reaction at temperatures of 150.degree.-300.degree. C., preferably 175.degree.-250.degree. C. Furthermore, the middle distillate process produces hydrocarbon oil mixtures that boil between 140.degree. C. and 370.degree. C., which is a higher boiling range than the products produced in the present invention. U.S. Pat. No. 4,608,450 reveals technology for a two-stage process for preparing C3 or C4 olefin tetramers using nickel-containing MFI. The process claimed involves reaction at higher pressures, e.g., 200 to 1600 psig (1.38 to 11.03 MPa), and lower temperatures, e.g., 80.degree.-450.degree. F. (27.degree.-232.degree. C.), than the process of the present invention. Furthermore, the process is not intended to produce aromatic hydrocarbons as is the process of the present invention. Finally, the process of the present invention involves reaction of the feedstock in one stage and thus is not a two-stage process for reaction of the feedstock as is the prior art. Thus, the prior art processes are distinctly different from the process of the present invention.
Several patents describe the aromatization of hydrocarbons using Ni on MFI or MEL zeolites. For example, U.S. Pat. No. 4,652,360 assigned to Mobil Oil, U.S. Pat. No. 4,347,394, assigned to Chevron, and EP 186,479 assigned to Mobil Oil, describe base-exchanged (Group IA or IIA metal component) zeolite catalysts having a Group VIII metal component for the aromatization of reformate feedstocks. The acid-catalyzed cracking activity of such catalysts is intentionally minimized by the addition of Group IA and/or Group IIA cations. Thus, the technology practiced in these patents differs from that of the present invention in that the catalyst of the instant invention is maintained in its acidic, or protic, form.
U.S. Pat. No. 4,717,782 and U.S. Pat. No. 4,740,645 assigned to Mobil Oil, disclose using a nickel containing MFI catalyst to oligomerize ethene in the presence of a reducing component such as hydrogen and a co-feed of water. The water is present in an amount to maintain the nickel component of the oligomerization catalyst in an oxidized state. Once the water co-feed is terminated, the Ni-MFI catalyst loses its selectivity advantages. This technology is significantly different from the present invention, however, in that the process of the instant invention does not require the continuous addition of water. Furthermore, the Ni-MFI of the present invention does not lose its activity benefits in the absence of water as a co-feed.
Mild steaming of shape-selective zeolites has been disclosed by Chester et al. in U.S. Pat. Nos. 4,429,176 and 4,522,929, as enhancing both the alpha activity and stability of such catalysts in acid-catalyzed reactions such as xylene isomerization. U.S. Pat. No. 4,559,314 to Shihabi, teaches that very highly siliceous shape-selective selective zeolites, which are inactive, can be activated by steaming the alumina bound zeolite. However, these patents do not recognize that nickel improves the activity of MFI zeolite after severe thermal or hydrothermal treatment.
3. Objects of the Invention
It is an object of this invention to convert non-aromatic compounds into aromatic compounds with a catalyst containing an acidic crystalline zeolite material and a Group VIIIA metal functionality.
It is a further object of this invention to produce aromatic hydrocarbons from non-aromatic compounds with a catalyst that maintains high activity after severe thermal and hydrothermal treatments such as are encountered in regeneration steps in processes for producing aromatic hydrocarbons.
These and further objects will become apparent as the description of the invention proceeds.